package com.stark.wechat.util;

import com.stark.wechat.exception.AesException;
import org.apache.commons.codec.binary.Base64;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

/**
 * AES 加解密工具类
 *
 * @author <a href="mailto:mengbin@hotmail.com">Ben</a>
 * @version 1.0.0
 * @since 2024/5/23
 */
public class AESUtil {

    /**
     * 对明文进行加密.
     *
     * @param text 需要加密的明文
     * @return 加密后base64编码的字符串
     * @throws AesException aes加密失败
     */
    public static String encrypt(String appId, String encodingAesKey, String text) throws AesException {
        ByteGroup byteCollector = new ByteGroup();
        byte[] randomStrBytes = getRandomStr().getBytes(StandardCharsets.UTF_8);
        byte[] textBytes = text.getBytes(StandardCharsets.UTF_8);
        byte[] networkBytesOrder = getNetworkBytesOrder(textBytes.length);
        byte[] appidBytes = appId.getBytes(StandardCharsets.UTF_8);

        // randomStr + networkBytesOrder + text + appid
        byteCollector.addBytes(randomStrBytes);
        byteCollector.addBytes(networkBytesOrder);
        byteCollector.addBytes(textBytes);
        byteCollector.addBytes(appidBytes);

        // ... + pad: 使用自定义的填充方式对明文进行补位填充
        byte[] padBytes = PKCS7Encoder.encode(byteCollector.size());
        byteCollector.addBytes(padBytes);

        // 获得最终的字节流, 未加密
        byte[] unencrypted = byteCollector.toBytes();

        byte[] aesKey = Base64.decodeBase64(encodingAesKey + "=");
        try {
            // 设置加密模式为AES的CBC模式
            Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
            SecretKeySpec keySpec = new SecretKeySpec(aesKey, "AES");
            IvParameterSpec iv = new IvParameterSpec(aesKey, 0, 16);
            cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv);

            // 加密
            byte[] encrypted = cipher.doFinal(unencrypted);

            // 使用BASE64对加密后的字符串进行编码
            return Base64.encodeBase64String(encrypted);
        } catch (Exception e) {
            throw new AesException(AesException.EncryptAESError);
        }
    }

    /**
     * 对密文进行解密.
     *
     * @param text 需要解密的密文
     * @return 解密得到的明文
     * @throws AesException aes解密失败
     */
    public static String decrypt(String appId, String encodingAesKey, String text) throws AesException {
        byte[] aesKey = Base64.decodeBase64(encodingAesKey + "=");
        byte[] original;
        try {
            // 设置解密模式为AES的CBC模式
            Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
            SecretKeySpec key_spec = new SecretKeySpec(aesKey, "AES");
            IvParameterSpec iv = new IvParameterSpec(Arrays.copyOfRange(aesKey, 0, 16));
            cipher.init(Cipher.DECRYPT_MODE, key_spec, iv);

            // 使用BASE64对密文进行解码
            byte[] encrypted = Base64.decodeBase64(text);

            // 解密
            original = cipher.doFinal(encrypted);
        } catch (Exception e) {
            throw new AesException(AesException.DecryptAESError);
        }

        String xmlContent, from_appid;
        try {
            // 去除补位字符
            byte[] bytes = PKCS7Encoder.decode(original);

            // 分离16位随机字符串,网络字节序和AppId
            byte[] networkOrder = Arrays.copyOfRange(bytes, 16, 20);

            int xmlLength = recoverNetworkBytesOrder(networkOrder);

            xmlContent = new String(Arrays.copyOfRange(bytes, 20, 20 + xmlLength), StandardCharsets.UTF_8);
            from_appid = new String(Arrays.copyOfRange(bytes, 20 + xmlLength, bytes.length),
                    StandardCharsets.UTF_8);
        } catch (Exception e) {
            throw new AesException(AesException.IllegalBuffer);
        }

        // appid不相同的情况
        if (!from_appid.equals(appId)) {
            throw new AesException(AesException.ValidateAppidError);
        }
        return xmlContent;
    }

    // 随机生成16位字符串
    public static String getRandomStr() {
        String base = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        Random random = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 16; i++) {
            int number = random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    // 生成4个字节的网络字节序
    private static byte[] getNetworkBytesOrder(int sourceNumber) {
        byte[] orderBytes = new byte[4];
        orderBytes[3] = (byte) (sourceNumber & 0xFF);
        orderBytes[2] = (byte) (sourceNumber >> 8 & 0xFF);
        orderBytes[1] = (byte) (sourceNumber >> 16 & 0xFF);
        orderBytes[0] = (byte) (sourceNumber >> 24 & 0xFF);
        return orderBytes;
    }

    // 还原4个字节的网络字节序
    private static int recoverNetworkBytesOrder(byte[] orderBytes) {
        int sourceNumber = 0;
        for (int i = 0; i < 4; i++) {
            sourceNumber <<= 8;
            sourceNumber |= orderBytes[i] & 0xff;
        }
        return sourceNumber;
    }

    static class ByteGroup {
        List<Byte> byteContainer = new ArrayList<>();

        public byte[] toBytes() {
            byte[] bytes = new byte[byteContainer.size()];
            for (int i = 0; i < byteContainer.size(); i++) {
                bytes[i] = byteContainer.get(i);
            }
            return bytes;
        }

        public ByteGroup addBytes(byte[] bytes) {
            for (byte b : bytes) {
                byteContainer.add(b);
            }
            return this;
        }

        public int size() {
            return byteContainer.size();
        }

    }

    /**
     * 提供基于PKCS7算法的加解密接口.
     */
    static class PKCS7Encoder {
        static int BLOCK_SIZE = 32;

        /**
         * 获得对明文进行补位填充的字节.
         *
         * @param count 需要进行填充补位操作的明文字节个数
         * @return 补齐用的字节数组
         */
        static byte[] encode(int count) {
            // 计算需要填充的位数
            int amountToPad = BLOCK_SIZE - (count % BLOCK_SIZE);
            if (amountToPad == 0) {
                amountToPad = BLOCK_SIZE;
            }
            // 获得补位所用的字符
            char padChr = chr(amountToPad);
            StringBuilder tmp = new StringBuilder();
            for (int index = 0; index < amountToPad; index++) {
                tmp.append(padChr);
            }
            return tmp.toString().getBytes(StandardCharsets.UTF_8);
        }

        /**
         * 删除解密后明文的补位字符
         *
         * @param decrypted 解密后的明文
         * @return 删除补位字符后的明文
         */
        static byte[] decode(byte[] decrypted) {
            int pad = decrypted[decrypted.length - 1];
            if (pad < 1 || pad > 32) {
                pad = 0;
            }
            return Arrays.copyOfRange(decrypted, 0, decrypted.length - pad);
        }

        /**
         * 将数字转化成ASCII码对应的字符，用于对明文进行补码
         *
         * @param a 需要转化的数字
         * @return 转化得到的字符
         */
        static char chr(int a) {
            byte target = (byte) (a & 0xFF);
            return (char) target;
        }

    }

    private AESUtil() {}

}
